The present invention relates to an automatic signature opener for opening continuously moving signatures as they are fed to a book sewer. The term "book sewer" as used herein includes any machine for attaching signatures together to form a book, the traditional way of attaching such signatures being to sew them together. The signatures themselves are primarily composed of large sheets which are folded a number of times, the final fold forming the spine of the signature. The signatures are normally stored in a stack, and in order to join them together in the book sewer, it is usually necessary to open the signature to the center in order to insert some part of the book sewer within the center of the signature, the usual procedure being to open the signature and to insert the signature over a saddle with its spine uppermost. The opening procedure is complicated by the fact that loose sheets can be inserted into various signatures of a book, and in order to open the signature to the center, a number of separate opening operations must be performed in order to raise the requisite number of sheets. Normal modern practice is to open the signature as the signature is being continuously conveyed, in order to be able to use continuously moving machinery without the changes in inertia that would occur if the signatures moved discontinuously.
The invention more specifically relates to an opener comprising conveying means for continuously conveying a succession of signatures along a conveying path and at least one operative member which engages an exposed face of a first part of the signature and draws the first part away from a second part of the signature to open the signature, a separating member for insertion between the first and second parts of the signature, to hold them apart, and releasing means for subsequently releasing the first part from the operative member. It will be understood that if one or more sheets of the signature have already been raised, said "first part" would not be the top sheet of the signature but would be the next sheet exposed for opening.
Such an opener is described in British Patent Specification No. 1,234,720, in which the operative member is a sucker which rotates about an axis spaced from and transverse to the conveying means, the releasing means being for cutting off the suction so that the first part of the signature is released from the sucker.
A specific problem arises with porous paper when sheets are being withdrawn from a stack or when signatures are being opened. There is a risk that the second sheet of the stack or the second sheet of the signature would also be picked up, and although this may not always occur, it occurs frequently enough to disturb production. If it does occur, two sheets would be fed instead of one or a signature would be opened in the wrong place. In addition, the provision of a sucker as well as the suction ducts and control gear for cutting off the suction, is relatively expensive.
It has been suggested in the past that an electrostatic effect can be used for picking up a sheet by inducing a high electrostatic charge on the operative member. However, this effect depends on the type of paper, and it is not possible to use the electrostatic effect with papers which conduct electricity to an appreciable extent.
According to the prior art, the use of a pressure-sensitive adhesive surface has been suggested for the specific purpose of removing individual paper sheets from a stack. Thus an oscillating member is used in U.S. Pat. No. 2,351,367, the member having an edge over which an adhesive tape is advanced step-wise; the successive sheets are delivered to feed rolls which remove the sheets from the pivoted member. British Patent Specification No. 961 371 discloses a like arrangement; the sheet is released from the adhesive either by holding the opposite end of the sheet so that the pivoted member pulls away from the sheet, or by using a pressure member which strips the sheet directly off the pivoted member. U.S. Pat. No. 2,919,129 discloses a somewhat similar arrangement in which the tape passes over a reciprocating roller which acts as the operative surface; in this case a short stripper arm pushes the sheet off the operative surface. British Patent Specification No. 928 559 discloses a like but more complicated arranged in which there are two rollers and in which the sheet is stripped from the rollers by withdrawing the rollers through openings in a pick-up plate. German Pat. No. 477,161 discloses the use of two parallel bars to which adhesive is applied by a roller, and French Pat. No. 1,445,891 discloses a somewhat similar arrangement using one bar.
German Pat. No. 462,025 discloses a very crude arrangement in which a guillotine for slitting envelopes open is provided with two sticky rollers for pulling the sides of the envelope apart, no arrangement being provided for stripping the envelope off the rollers apart from the resistance of the envelope itself.
None of these items of prior art relate to opening continuously moving signatures being fed to a book sewer; when moving signatures are being opened, the opening procedure is complicated by the movement of the signature itself, and the position of the signature upon the conveying means must not be substantially altered as any substantial alteration of the signature can cause false registration of the signature when entering the sewing machine or skewing of the signature to such an extent that it cannot be fed forwards to the sewing machine.